1. Field of the Invention
The present invention relates to a polymeric fluorescent substance and more specifically a polymer light-emitting device using the same.
2. Description of Related Art
An organic electroluminescence device is an device using mainly an organic compound of lower molecular weight as a light emitting material, and there are a lot of trials reported regarding device structures, organic fluorescent dyes and organic charge transporting materials since the electroluminescence device has characteristics that it is driven at lower voltage, has higher luminance and can easily give light emission of many colors as compared with conventional inorganic electroluminescence devices [Jpn. J. Appl. Phys., 27, p. L269 (1988), J. Appl. Phys., 65, p. 3610 (1989)].
Apart from organic electroluminescence devices using mainly an organic compound having lower molecular weight, there is a polymer light emitting device (hereinafter, referred sometimes to as polymer LED) using a light emitting material having higher molecular weight (hereinafter, referred sometimes to as polymeric fluorescent substance). WO9013148, JP-A No. 3-244630, Appl. Phys. Lett., 58, p. 1982 (1991) and the like disclose polymer LEDs using a polymeric fluorescent substance, poly(p-phenylenevinylene) (hereinafter, referred to as PPV), or a derivative thereof in a light emitting layer.
Polymeric fluorescent substances and derivatives thereof have a merit that they can be dissolved in a solvent, and can form a light emitting layer by an wet film-forming method.
As the polymeric fluorescent substance used in these polymer LEDs, polyfluorene (Jpn. J. Appl. Phys., 30, p. L1941 (1991)), poly-p-phenylene derivatives (Adv. Mater., 4, p. 36 (1992)), and the like are also reported, in addition to the above-mentioned poly(p-phenylenevinylene) and derivatives thereof.
Regarding the polyfluorene derivative, J. Mater. Sci. Mater. Ele., 11, p. 111 (2000) describes copolymers composed of a fluorene repeating unit and a repeating unit of stilbene, phenylene, 1,4-naphthalene, aromatic amines and the like in which a cyano group is substituted on vinylene, and polymer LEDs using these copolymers.
An object of the present invention is to provide a polymeric fluorescent substance containing an arylene vinylene structure and a fluorene structure and manifesting strong fluorescence, and a polymer LED of high performance which can be driven at lower voltage with high efficiency, using this polymeric fluorescent substance.
The present inventors have intensively studied in view of such conditions, and resultantly found that a polymeric fluorescent substance manifesting fluorescence in solid state and having a polystyrene-reduced number-average molecular weight of 103 to 108 wherein the polymeric fluorescent substance contains one or more of segments represented by the following formula (1) and one or more of repeating units represented by the following formula (2) shows strong fluorescence and a polymer LED of high performance which can be driven at lower voltage with high efficiency is obtained using the above-mentioned polymeric fluorescent substance, leading to completion of the invention.
Namely, in accordance with the present invention there is provided [1] A polymeric fluorescent substance manifesting fluorescence in solid state and having a polystyrene-reduced number-average molecular weight of 103 to 108 wherein the polymeric fluorescent substance contains one or more of segments represented by the following formula (1) and one or more of repeating units represented by the following formula (2): 
[wherein, Ar1 and Ar2 each independently represent an arylene group or a divalent heterocyclic compound group. R2 and R3 each independently represent a group selected from the group consisting of a hydrogen atom, alkyl groups, aryl groups, heterocyclic compound groups and cyano group. R1 and R4 each independently represent a group selected from the group consisting of alkyl groups, alkoxy groups, alkylthio groups, alkylsilyl groups, alkylamino groups, aryl groups, aryloxy groups, arylsilyl groups, arylamino groups, arylalkyl groups, arylalkoxy groups, arylalkylsilyl groups, arylalkylamino groups, arylalkenyl groups, arylalkinyl groups, monovalent heterocyclic compound groups and cyano group. The symbols a and c each independently represent an integer of 0 to 4, and b represents an integer of 1 or more. When b is 1, a and c do not represent 0 simultaneously. When b is 2, at least one of groups R2 and R3 represents a group other than a hydrogen atom and cyano group. When b is 3 or more, a and c do not represent 0 simultaneously if both of R2 and R3 are a hydrogen atom. When a is 2 or more, a plurality of R4s may be the same or different. When c is 2 or more, a plurality of R4s may be the same or different. R1 to R4 may be connected to form a ring. Further, when R1 to R4 are a group containing an alkyl chain, one or more of a methyl group, methylene group and methine group constituting this alkyl chain may be substituted with a group containing a hatero atom], 
[wherein, R5 and R6 each independently represent a group selected from the group consisting of a hydrogen atom, alkyl groups, aryl groups and monovalent heterocyclic compound groups. R7 and R8 each independently represent a group selected from the group consisting of alkyl groups, alkoxy groups, alkylthio groups, alkylsilyl groups, alkylamino groups, aryl groups, aryloxy groups, arylsilyl groups, arylamino groups, arylalkyl groups, arylalkoxy groups, arylalkylsilyl groups, arylalkylamino groups, monovalent heterocyclic compound groups and, cyano group. The symbols k and 1 each independently represent an integer of 0 to 3. When k is 2 or more, a plurality of R7s may be the same or different. When 1 is 2 or more, a plurality of R8s may be the same or different. Two or more of R5 to R8 may be mutually connected to form a ring. Further, when R5 to R8 are a group containing an alkyl chain, this alkyl chain may be interrupted with a group containing a hetero atom.] The present invention also provides [2] A polymer light emitting device comprising at least a light emitting layer between a pair of electrodes composed of an anode and a cathode at least one of which is transparent or semi-transparent wherein the light emitting layer contains a polymeric fluorescent substance according to [1].
The present invention provides a flat light source, a segment display, and a dot matrix display all obtained by using the polymer light emitting device. The present invention also provides a liquid crystal display obtained by using the polymer light emitting device as a back-light.